Thermionic valve circuit arrangement



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THERMIONIC VALVE CIRCUIT ARRANGEMENT Filed May 25, 1.934 2 Sheets-Sheet1 VOLT/46E 04 6,9/0 0F WLVE f2 50 ff man@ am 6,9/0 of M40/f a .fifa/voM4455 INVENTOR f//er Aff 00m/6577 eg/sfi- 50E/V006# ATTORNEY 23, i3?, H.M. DowsETT ET AL www THERMIONIC VALVE CIRCUIT ARRANGEMENT Filed May 25,1954 2 ShetS-Shee'k 2 Mann INVENTOR HAIQEY M. 00h/5577 5g/1557' F.EA/006# ATTORNEY Patented Mar. 23, 1937 UNITED STATES PATENT yOFFICEHarry Melville, Dowsett and Ernest Frederick Goodenough, London,England, assignors to Radio Corporation of America, a corporation ofDelaware Application May 25,

1934, Serial No. 727,446'

In Great Britain April 24, 1933 3 Claims.

This invention relates to thermionic valve circuit arrangements and moreparticularly to circuit arrangements wherein a load is driven orenergized from a thermionic valve, said load being 5 of such impedanceas not to match" the said valve.

More specifically, though not exclusively, the invention relates toarrangements suitable for use in television and other facsimilereceivers wherein a load device constituted by a neon or other electric`glow discharge tube is energized from a valve, the light from said tubebeing employed to reproduce in any manner well known per se, atelevision or other picture.

Although as above stated, the invention is not limited to arrangementsinvolving neon or similar electric glow discharge tubes, the saidinvention will be particularly described with reference to itsapplication to such arrangements since it is primarily designed for usein connection with such arrangements.

At the present time it is usual in television and like receivers tooperate a picture building neon or like tube by means of a thermionicvalve, to Whose grid circuit the television signals are fed, said tubebeing either in series or in parallel with said valve. For example inone well known arrangement a neon tube is connected in series with asource of anode potential between the anode and cathode of a thermionicvalve to whose grid circuit the television or other signals are applied.This is a series arrangement. In another well known arrangementtheparallel arrangement-a neon or like tube is directly connected betweenthe anode and cathode of the valve to whose grid circuit the televisionor other signal potentials are applied, the anode of r'said valve beingconnected to the positive terminal of a source of anode potentialthrough a choke in series with a resistance.

Figures 1 and 2 are curves indicating the distortion that results fromthe use of a glow discharge tube in the output circuit of a valve.

Figure 3 shows schematically an arrangement for correcting thisdistortion.

Figures 4-7 show more conventional circuits for accomplishing the resultof Figure 3.

Now in general the impedance of a neon or similar electric glowdischarge tube, such as can be employed for picture reproduction is verydifferent from that which would be necessary to match the impedance ofan ordinary thermionic valve, the said tube impedance being generallymuch lower than that of a valve. For

example, the impedance of a so-called crater neon tube may be taken tobe, in general, of the order of 200 ohms. As a result of this fact, moreor less series distortion occurs when either the series or the parallelarrangement hereinbefore described is employed. 'I'he nature of thisdistortion will be readily appreciated from Figures 1 and 2 of thedrawings, Figure 1 being a graph connecting tube current (ordinates)with voltage applied to the grid of the valve (abscissae) when the tubeand valve are in lseries arrangement hereinbefore described. SimilarlyFigure 2 of the drawings is a corresponding graph of the resultsobtained with the parallel arrangement, tube current (ordinates) beingagain plotted against grid voltage (abscissae). In both the said Figures1 and 2, En and I0 are respectively the normal mean potential on thegrid of the valve and the resultant current through the tube and it willbe seen that the current change (In to Iz) obtained for a grid voltageswing from En to E2 is quite different from the current change (In toI1) obtained when a grid voltage swing of like magnitude but in theother direction takes place between the valve En and E11. In the seriescase the current change for a grid voltage change Eo-Ei is considerablygreater than the current change for a grid Voltage swing Eli-E2 while inthe parallel case a distorting effect which is opposite in nature occursi. e. the current change for a grid voltage swing Eri-E1 is considerablyless than the current change for a grid voltage swing Eri-E2.

The present invention has for its object to avoid the forms ofdistortion above referred to and this object is achieved by employing acomposite arangement which may be regarded as consisting of series andparallel arrangements in combination and which is such that thedistorting effect due to the series feature of the arrangement issubstantially annulled or oir-set by the distorting eiect due to theparallel feature of the said arrangement.

ccording to this invention, a load device is fed by the parallel methodfrom one valve and by the series method from another and the signal crother voltages applied to the grids of these valves are arranged to bein opposite phase.

The invention is illustrated in and further explained in connection withFigures 3 to '7 of the accompanying drawings.

Referring first to Figures 3 and 4 a neon or other glow discharge tube5, employed for example as a reproducing device in a television or otherreceiver, is connected in series with a thermionic valve 4 and also inparallel with a thermionic valve 3 the parallel feed being obtained inmanner well known per se, by means of a choke 'i and resistance 8connected in series with one another between the anode of the valve 3and the positive terminal -l-HI' of the common driving source of anodepotential. .Resistances 9 and I0 (see Fig. 4) are connected across thetube 5. 10 The resistance 9 serves to bias the Avalve 4. Input signals,for example television signals, are applied to the grid of a valve Iwhose anode is coupled as illustrated to the grids of thermionic valves2 and 3. Of these two valves the valve 2 reverses the phase of thesignals and applies its output, as illustrated, to the grid of the valve4 while the valve 3 is, as above described, a parallel feeding Valve. Byvariation of the grid bias applied to the valves 3 and 4 and by varyingthe resistance 8 above referred to, the anode current of the said valves3 and 4 as well as the current through the tube 5 may be adjusted todesired values. Since, as above stated, the purpose of the valve 2 isprincipally to reverse the phase of the signal, the signal input to thegrid of this valve may, if desired, be initially attenuated by adjustinga potentiometer 6 associated as shown with the grid circuit of the saidvalve 2.

Figure 3 of the drawings is a theoretical diagram representing thearrangement which is shown in a more conventional manner in Figure 4,the parts in Figure 4 being indicated by the same reference numerals asare employed in Figure 3 and the arrows in Figure 3 indicating thedirections of the steady currents. It will be obvious from Figures 3 and4 that the picture may be reversed from positive to negative or viceversa by reversing the grids of the valves 3 and 4. In Figure 3 the leadfrom the grid of the valve 4 is marked to iirst phase and the lead fromthe grid of the valve 3 is marked to second phase in order to indicatethe phase reversal which is effected.

Instead of employing an additional valve for phase reversal i. e. forsecuring the necessary phase difference between the signals applied tothe grids of the valves 3 and 4, transformers may be employed. Two sucharrangements are shown in Figures 5 and 6*. of the drawings. In the saidFigure 5 a transformer Il is employed and its secondary is so connectedthat the picture signal is impressed on the grid of the valve 4 inopposite phase from the signal impressed on the grid of the valve 3while in the said Figure 6 the desired result is achieved by employing atransformer l2 having two secondary windings as shown, one windingfeeding the valve 3 and the other feeding the valve 4 so as to securethe desired reversal of phase. The arrangement shown in Figure 7 of thedrawings is a modification of the arrangement shown in Figure 4. In theaccompanying drawings valves 3 and 4 connected in series are employedand a choke 1 and resistance 8 which are connected in series with oneanother and with the neon tube 5 are isolated, as regards directcurrent, by means of a condenser Il. The resistance 9 provides grid biasfor the valve 4.

We claim:-

1. In a television, facsimile or the like receiver, a glow dischargedevice, a space discharge device provided with an anode, a cathode and asignal grid, a source of space current, a series circuit comprising thespace path of said space discharge device, said glow discharge deviceand said source of space current, a second space discharge deviceprovided with an anode, a cathode and a signal grid, means for supplyingthe anode of said second space discharge device with anode potentialcomprising said source of space current, said source being connected tothe anode of the second space discharge device through an inductive andresistive impedance circuit, a circuit including said glow dischargedevice directly connecting the anode and cathode of said second spacedischarge device and means for applying picture signals in phaseopposition to the two grids of said two space discharge devices.

2. A circuit arrangement as described in the next preceding claimfurther characterized by that the glow discharge device is connected inshunt with a resistance element, and means are provided for utilizingthe voltage drop across a part of said resistance for biasing the gridof the iirst named space discharge device.

3. In a thermionic tube driving circuit for glow discharge tubes and thelike of the type wherein distortion of the signal energy is introduceddue to the fact that the impedance characteristic of the glow dischargetube can notvbe matched accurately to the impedance characteristic ofthe.A

thermionic tube, means for compensating for the distortion of the signalenergy comprising a pair of thermionic tubes each thereof being providedwith an input circuit and an output circuit, the output circuit of eachtube including a source of space current, means for connecting the glowdischarge device in the output circuit of one of said tubes so as toform a series circuit comprising the space path of the tube, the glowtube and the source of current, means for connecting the glow dischargedevice in the output circuit of the other of said tubes so that saidglow discharge device is in parallel with the space path of said othertube as respects the source of space current, means for impressingsignaling energy upon both of said input circuits, the signaling energyimpressed upon one of said circuits being in phase opposition to thesignaling energy impressed upon the other thereof.

HARRY MELVILLE DOWSETT. ERNEST FREDERICK GOODENOUGH.

